The present invention relates to a rotary-to-linear actuator for converting rotational motion into linear motion and outputting it, a linear motion shaft mechanism for making a drive shaft operate through the linear motion inputted from the rotary-to-linear actuator, a variable valve actuation mechanism for changing the valve parameters of the same valve by the linear motion inputted from the rotary-to-linear actuator by making one of intake valve and exhaust valve as an engine valve and an engine in which the variable valve actuation mechanism is mounted.
A rotary-to-linear actuator has a rotary-to-linear conversion mechanism for converting rotational motion inputted into linear motion and outputting it and a motor for inputting the rotational motion to this rotary-to-linear conversion mechanism. A rotary-to-linear conversion mechanism includes the combination of a ring shaft for moving a rotational motion through the motor, a sun shaft which is disposed interior of the ring shaft and functions as an outputting shaft of the motion conversion mechanism, and a plurality of planetary shafts which are disposed between the ring shaft and the sun shaft and are engaged with a screw of the ring shaft and a screw of the sun shaft (see Japanese Laid-Open Patent Publication No. 10-196757).
In these rotary-to-linear actuators, when the ring shaft performs rotational motion through the motor, the sun shaft is to perform the linear motion through this planetary motion as well as the planetary shafts perform the planetary motion around the sun shaft.
The above-described rotary-to-linear actuator can be applied to a linear motion shaft mechanism equipped with a drive shaft which is capable of performing the linear motion. As a linear motion shaft mechanism, for example, a variable valve actuation mechanism of an engine described in Japanese Laid-Open Patent Publication No. 2003-41977 is known. In the case where the above-described rotary-to-linear actuator is applied to this variable valve actuation mechanism, the valve parameters of an engine can be changed by performing the displacement of a camshaft through the linear motion of the sun shaft.
(A) In the case where a rotary-to-linear actuator is applied to the linear motion shaft mechanism, there is fear that the lowering of the life of the actuator is caused by promoting the abrasion of the respective components of the rotary-to-linear conversion mechanism, which is caused by the oscillation of the sun shaft.
The present invention has been completed by considering these circumstances, and an object of the present invention is to provide a rotary-to-linear actuator which can suppress the oscillation of the output shaft, a linear motion shaft mechanism, a variable valve actuation mechanism, and a variable valve engine.
(B) In a rotary-to-linear actuator, in order to precisely perform the conversion from the rotational motion to the linear motion by the rotary-to-linear conversion mechanism, it is necessary to regulate the thrust displacement of the ring shaft. Then, it is also considered that the ring shaft is supported by the housing body of a rotary-to-linear actuator in a axial direction, however, in this case, since it is required that the thickness of the outer wall of the housing body is sufficiently large because it is subjected to the thrust load of the ring shaft, it is difficult to achieve the miniaturization of an actuator.